The present invention relates to tape storage systems, and more specifically, to a high density pattern detector for use with tapes having hybrid servo patterns.
Timing-based servo (TBS) is a technology developed specifically for linear tape drives in the late 1990s. In TBS systems, recorded servo patterns include transitions with two different azimuthal slopes. An estimate of the head lateral position is derived from the relative timing of pulses generated by a servo reader reading the pattern.
In a TBS format, the servo pattern is prerecorded in several bands distributed across the tape, typically five or nine bands. Data is recorded in the regions located between pairs of servo bands. FIG. 3 illustrates the tape layout for five servo bands and four data bands, as specified in the linear tape-open (LTO) format and IBM Enterprise format. In read/write heads of IBM LTO and Enterprise tape drives, two servo readers are normally available per head module, from which longitudinal position (LPOS) information as well as a position error signal (PES) may be derived. Optimum detection of the TBS patterns is achieved by a synchronous servo channel employing a matched-filter interpolator/correlator, which ensures optimum filtering of the servo reader signal.
With the increase in track density that is envisioned for future tape media and tape drives, controlling the lateral position of the head and its skew with respect to tape by using feedback generated by reading the TBS patterns might not be sufficiently accurate to ensure adequate positioning accuracy of the data readers and writers that move along data tracks. Furthermore, the repetition rate of the head lateral position estimates might be too small to guarantee proper track-following operation at very low tape velocity, or to support future actuators with large bandwidths.